Multicomponent reactant materials are widely used in manufacturing. Some of these reactant materials must be contacted shortly before application, because of the speed of the reaction. Among these materials are those making polyurethane foam, and elastomeric coatings, resin formulations, and the like, as described in U.S. Pat. Nos. 4,867,346, issued Sep. 9, 1989, and 5,170,939, issued Dec. 15, 1992 in the name of Martin.
A reactant component of some foam formulations tends to harden even in the absence of the other component or a catalyst, and the presence of even a minuscule amount of the other reactant material at one end of a quantity of the hardenable component will result in progressive hardening of the entire hardenable mass. The problems of spraying such materials is compounded by the high pressures, which can range up to 3000 pounds per square inch (PSI), necessary to cause flow of the reactant materials, and to forcefully eject the reacted material from the spray nozzle. U.S. Pat. No. 4,913,317, issued Apr. 3, 1990, in the name of Wernicke, is directed, in part, toward the problem of multicomponent foam tending to harden even in the absence of a catalyst or second reactant material, and includes first and second mechanically synchronized rotary valves, each of which is coupled to a source of one of the reactants and a source of purging gas, and which, when rotated, pass either the reactant component or the purging gas to a mixing chamber. The two valves of this arrangement are difficult to synchronize so as to start and stop the flow of reactant material to the mixing or reacting chamber and nozzle.
The synchronization problem of the Wernicke arrangement is solved by a ball valve spray gun as described in the above-mentioned Martin patent. The Martin arrangement uses a rotary ball valve having a port for each component, and containing a wye (Y) at which the two reactant materials meet. Rotation of the ball simultaneously moves both reactant ports of the ball, which, with proper alignment of the ball with its associated source apertures, necessarily results in synchronous operation.
Another of the problems associated with spray guns for multicomponent reactant materials is that of disassembly for cleaning. Even with a gas purge, some reacted material will inevitably adhere to internal portions of the dispensing apparatus or spray gun, and such material will build up with time, and interfere with operation. This interference may be in the form of changing the spray pattern, and may occur relatively frequently. This problem is addressed in the prior art by using tetrafluoroethylene (TEFLON) or other low-adherence material. However, buildup of reacted material still occurs, even with the best of materials, so frequent cleaning of the interior of the spray gun is required. The Martin ball valve arrangement requires disassembly of the ball from its complex seats, which include metallic rings. The metallic rings prevent excessive cold-flow of the tetrafluoroethylene under the high pressure, since portions of the tetrafluoroethylene seat might flow into the ports, and be shaved off when the valve is rotated. U.S. Pat. No. 4,867,346, issued Sep. 19, 1989 in the name of Faye et al., discusses this disadvantage of the use of tetrafluoroethylene for high-pressure applications in the context of a valve rod.
Simplified disassembly for cleaning is a feature of the foam spray gun described in U.S. Pat. No. 4,708,292, issued Nov. 24, 1987 in the name of Gammons. In the Gammons arrangement, an easily removable and replaceable combination mixing-chamber and nozzle, formed from an inexpensive, deformable, low friction material, is held by pressure against ports which admit the reactant materials, and flow of the materials is controlled by a valve rod extending within the mixing chamber of the combination mixing-chamber and nozzle. This arrangement has the disadvantage that, when the flow is stopped by the valve rod, the reactant material in each port has been in contact with the other reactant, and may harden. This portion of the material may not be accessible for cleaning by removal of the mixing-chamber/nozzle. The valve stem is also required to conform to the internal shape all the way into the spray tip, otherwise the reactive spray materials will harden, thereby causing resistance to repeated operations, and blocking the tip orifice.
An improved spray gun apparatus is desired.